A Hack for “Unknown or expired link”

October 28, 2009

You’re using a web site, you fill in a big long form, and, upon submitting, you get “Unknown or expired link.” Why does this happen? The short[1] explanation is that the web site gave you a hidden code to submit with your form, and while you were typing, your code expired. If you hit “Refresh” to get a new code, your browser will probably throw away the contents of your form. You’re lucky you can hit “Back” from the “Unknown or expired link” page.

What to do?

Choice number 1: Copy out your form contents, refresh the page, and paste the contents back in. Slow, boring and painful.

Choice number 2: Get a new code and edit your current page to use it. Fast and fun!

How to get a new code: Open a new browser window, go to the page with the form, use “View source”, find the form you were filling in, find the hidden field in the form with a weird value, and copy the strange value.

How to edit your current page to use it: Go to the window where you’ve filled in your form, pop open your DOM editor, find the weird hidden field, and replace its value with your new code. Now when you submit your form, it will be using a fresh code!

OK, so maybe it isn’t easy, but at least it’s fast.

[1]: The long explanation is that the web site is probably using a continuation-passing style for managing client-side state and it garbage-collected your form submission continuation. I didn’t think you wanted to know.

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One Response to “A Hack for “Unknown or expired link””

  1. Reynold Xin Says:

    It would be helpful to have a firefox entension written for this. You don’t even need to guess the session key. Just save the entire form. Ask the user to “reproduce” the page. And “paste” the saved content back. The key is not to lose the unsvaed form content.


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